what is kalvin and color temperature?
Posted 27 February 2009 - 09:44 AM
Posted 27 February 2009 - 10:10 AM
K*e*lvin is basically a description based on the absolute temperature scale equivalent, of the Celsius temperature of how hot you would have to heat a "black body", like an iron rod in an oven, to get it to emit a certain color of light.
It basically has to do with the warmth or coolness of the "white" of the light your black body is emitting.
Counter-intuitively, the "hotter" the Kelvin temperature gets, the "cooler" the light gets (you get more perceived blue the higher the number goes and more red the lower the Kelvin temperature goes).
One of the drawbacks of Kelvin is that the number isn't proportional depending on what temperature you are at. In simple English the lower the temperature is, the more perceptable a 100-degree shift will be. So, if you are going from say 5600K to 6000K, the shift will actually be much smaller than, say, 2600 to 3000K.
To counter this non-arithmetic behavior, taking the MIcro-REciprocal Degree measurement (MIRED), effectively cancels out this behavior and renders an (almost) absolute filtration change factor that is sometimes used with colored glass filters. So basically, just think of MIRED as another way of expressing Kelvin in terms of an absolute filtration change factor (micro-reciprocal is a fancy way of saying Kelvin times the inverse of a million: 1/1,000,000).
I didn't 'do a good job of putting that in simple English, but hopefully that is clear-enough for you!
One last note, here are a couple of approximate Kelvin temperatures of different light sorces:
Light bulbs: Under 3,000K (the lower the wattage, the lower the Kelvin temperature)
Movie lights: 3,200K
Type A amateur photoflood lighting: 3,400K
Fluorescent lighting: ~4,000K (varies with different types)
Direct sunlight: 5,500K
Skylight (shade or cloudy): 6,000 to up to 10,000K
So, notice how the Kelvin number climbs "faster" and "faster" the higher up the scale you get, hence the need for MIRED. While a 3,200 to 3,400K change might be enough to necessitate putting a correction filter on a lens with tungsten (3,200K-balanced) film, a 5,500K to 6,000K will often be small enough to be shot un-filtered.
Posted 27 February 2009 - 10:52 AM
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